Process of cracking naphtha and heavier oils in the vapor phase



Oct. 8, 1935. A. P. sAcHs l 2,016,297

PROCESS OF CRACKING NAPHTHA AND HEAVIER OILS INv THE VAPOR PHASE Filed Oct.- 2'7, 1 955 SUPE'PHEATEP INVENTOR AAHE/F7' l? ACHS BY /M ATORNEY f Patented Oct. 8j, 1935 PROCESS OF CRACKIN G NAPHTHA HEAVIER OILS IN THE VAPOR PHASE Albert P. Sachs, Brooklyn, N. Y., assignor to Petroleum Conversion Corporation, New York, N. Y., a corporation of Delaware l Application october 27, 1933, serial No. 695,408 s claims. (ci. 19e-sc) l The present invention relates to improvements in cracking hydrocarbon oils in the vapor phase to produce motor fuels of the gasoline type and more particularly to improvements in the type of process described in the patent to Beardsley and Colonyv #1,842,318, dated January 19, 1932.

In this type of process the oil to be cracked is vaporized and the vapor, preferably superheated,

is mingled with a heated gaseous heat carrier in 10 a reaction chamber, the temperature of the'heat carrier gas being sufficient lto bring about cracking of the oil vapor with which it is mingled. In

a further development of the process' as exemplified inthe patent to Beardsley #1,883,744 the products from the reaction chamber are scrubbed with an oil containing comparatively heavy fractions, which oil may be in whole or in part the stock charged to the system, the purpose of this step being on the one hand to remove from the cracked products a portion of their heat and also small quantities of free carbon which may be entrained as well as tar and very heavy ends, and

on the other hand, to effect a fractionation of the stock introduced to the system at this point.

Thus. conditions are maintained so that the overhead distillate from the scrubber contains not 4only the vapors of the motor fuel formed in thev cracking zone but also the vapors of the oil to be cracked. The latter are dropped out in a suitable condensing unit or rectifier and are then fed to a vaporizer which furnishes the reaction chamber with vapors to be cracked.

'I'he present improvement is founded upon my discovery that the output of a plant of the fore# going type designed to crack heavy oil, e. g., gas

oil or heavier, can be materially increased if along with the heavier oil thereis added to the systemA a quantity of naphtha to be cracked, whereby the output capacity of the system-in gasoline can be materially increased. Naphtha while having an end boiling point not greatly different from that of gasoline is not suited for blending with gasolinev because of its unsatisfactory boiling range and generally its objectionably low anti'- knock rating. It is therefore desirable to reform the naphtha by cracking it into gasoline. Because of the nature of the cracking process on which my invention is an improvement and of the comparatively high volatility of the naphtha as 5 compared with gas oil, for example, it is possible to operate the system with the usual amount of the heavy oil cracking stock plus a large quantity of naphtha without having to increase the capacity of any part of the cracking system other than 5 possibly the gasoline condenser. The reasons for this are as follows: In crackingoil in the vapor phase, a large proportion of the total heat required goes to furnish the latent heat of vaporization of the oil. Because of this fact that so much heat must be supplied at one point in 5 the system, it is extremely diiiicult to increase the capacity of the system as a whole without installing additional vaporizing capacity. However, when 'the heavier oil, as for example gas oil, is diluted with a more volatile oil such'as l0 naphtha, the vaporization of the mixture is greatly facilitated, nrst, because the average boiling point of the mixture is much lower than the average boiling point of the gas oil, and second, because the naphtha when'vaporized acts to reduce l5 the partial pressure of the gas oil, or, in other words, functions in the manner of steam to' facilitate vaporization. Thus, for example, if the capacity of a given vaporizer is one hundred gallons of fresh gas oil charge per unit of time, such a 20 vaporizer can be caused to furnish vapor corresponding to one hundred gallons of fresh gas oil charge plus that corresponding to fifty gallons ofnaphtha per unit of time without increasing the fuel consumption substantially.. Now, of 25 course, the temperature of the mixture of the vapors leaving the .vaporizer is correspondingly less than the temperature ofthe gas oil vapor alone would be but this deficiency in heat units can be made up in the superheating step which 30 follows since a gas superheater has much greater flexibility and is much more capable of being overloaded `than is a vaporizer. Furthermore, suflicient heat, or as it is generally termed, superheat, may be imparted to the vapor mixture in 35 this manner so as to render it unnecessary to increase the ratio of carrier gas to oil vapor. Also by raising the crackingtemperature slightly, say by 5 to 10 F. as by increasing the vsuperheater temperature and/or the heat-carrier gas 40 temperature, the rate of ilow of the gas mixture through the reaction chamber can be increased so as to correspond with the'increased velocity of the cracking due to the 5 or 10 F. higher temperature, the reaction velocity doubling for each 22 F. increase in temperature. This slightly higher temperature is, moreover, of advantage in that at a temperature still satisfactory for the cracking of gas oil it insures a high conversion of the naphtha, e. g., 3% or above (while insur- 50 ing a 30% conversion of gas oil for example), which is desirable since, as above mentioned, the

' unconverted naphtha has a low anti-knock rating and its presence in gasoline is .therefore to be kept at a minimum. .5

A further advantage of cracking the gas oil and naphtha together is that less heat is lost by radiation than would be the case if the two were cracked separately.

My invention will be best understood by ref-iv erence to the following detailed description taken with the annexed drawing illustrative of a plant embodying my invention.

Referring to this drawing, the course of the heavier `oil will be first described. Here this charging `stock, which may be gas oil or an oil containing both heavier and lighter ends than gas oil, is fed from a source of supply l through pipe il into a scrubber I2 wherein it comes into contact with the hot products from the reaction chamber I4 fed therefrom through pipe I5. In the scrubber a portion of the heat in the reaction products is abstracted and the'tar and carbon and such very heavy ends as are present are dropped out and the hot oil residue is removed fromY the scrubber' through a pipe I1.

l'I'lie heat in this oil is recovered in large part lwhich it is desired to crack subsequently are vaporized. 'Ihe overhead distillate so produced is then led from the scrubber through pipe 2| into a rectier 22 wherein the ends heavier than the motor fuel are dropped out. In order to maintain the proper temperature within the rectifier 22 a portion of the residue is removed through pipe 23, is cooled in a cooler 2l, and pumped back `again into the top of the rectiiler through a pipe 25. 'I'he vapors escaping condensation leave the rectifier through pipe 21 by means of which they pass to a condenser 28', the condensate being passed to an accumulator 29 through a pipe 30 while the uncondensed vapors pass from the condenser through a pipe 3| into the top of accumulator 29 and thence g through a pipe 32 to an absorber. wherein the ther cracking.

residual light ends are separated out, after which the stripped gas passes to a gas holder 36 storing the gas produced in the system. The gas holder 36 constitutes a source of supply of gas not only for the cracking reaction but for various fuel purposes needed in the system. 'The liquid condensate from the rectifier 22, which contains the heavier ends to be cracked, is then withdrawn through pipe 30 leading to a' vaporizer 40. The

naphtha'to be cracked which may be stored in tank 4I is alsoadmitted (after being suitably preheated, if desired, conveniently from a source of waste heat within the system, not shown) 'to the vaporizer 40, through pipe lia leading into pipe 3l. It will be noted that the material leaving the rectifier 22 through pipe 38 will contain both the fresh gas oil which has been redistilled and the gas oil that' has been recycled for fur- The vapor formed is separated from the unvaporized liquid in the flash drum I2 whereupon the vapor leaving such drum is superheated in the superheater 4l, after which it passes through pipe 45 to the top of the reaction chamber Il. At the same time a n quantity'of heat-carrier gas is being heated up by one of the hot blast stoves 50 (or other heating device), such gas being admitted to the proper stove from pipe I1 and the hot gas is withdrawn through pipe I, by means of which it is discharged into the reaction chamber. It

- but substantially no recycling with respect to the will be understood that the battery of hot blast stoves 50 is arranged so that there is at all times a continuous supply of hot 4gas to the reaction chamber.

When the amount of gas oil being cracked is 5 equal to the capacity of the vaporizerfor gas oil alone, I may add to this a quantity of naphtha up to 50% by weight of the freshgas oil charge without increasing the burden on the vaporizer. It will be noted that since a conversion of the naphtha of 90% or over is obtained, as compared with a 30% conversion of the gas oil alone on one pass, in such a case there will be the usual amount of recycling with respect to the gas oil naphtha fraction. Thus the vaporizer will have to handle not an additional 50% by weight, but, if the recycle ratio of the gas oil alone is one part of recycle gas oil to one part of fresh feed only more by weight. But the total 125% by weight of the normal" charge will all vaporize at a considerably lower temperature than for gas oil alone so that the added heat burden or vaporizer load will be far less than 25% and for practical purposes may be` disregarded. The 25 temperature of cracking will ordinarily vary from 950 to 1050 F. although these limits are not critical, and where the system has been adjusted 'to operate on gas oil alone ata given range of cracking temperature, the cracking temperature to be chosen for the mixture of gas oil and naphtha may ordinarily be from 5 to 10 or more higher as above stated. The temperature oi the vaporized gas oil alone would be ordinarily about 800 F. while the temperature of the vaporized 35.

mixture of four parts gas oil and one part napha. tha for example will ordinarily be less than '100 F. This vapor mixture is lpreferably superheated to a temperature of 930' F. to 980 F. or higher, although lower temperatures as for exo ample 850 may be employed. This mixture may then be brought into contact with heatcarrier gasvof the type produced in the system, which may have a temperature of 1150 F. in the quantity of one pound of vapor mixture to 5 one-half pound of heat-carrier gas.

It will be understood that by gas oil is meant any oil having an initial boiling range of from 450 to 500 F. or higher. Furthermore, since gas oil .itself is an overhead distillate, all or a 50,

portion of the fresh feed may be admitted directly to the vaporizer I0, preferably after being preheated in some convenient manner. In case a large proportion of the gas oil is added to the vaporizer directly, the oil used for scrubbing will after the system has reached a steady state 'consist of the heavier fractions which are produced from any cracking stock simultaneously with the desired gasoline fractions.

AThe above stated conditions have been by way of example and may be varied somewhat without departing from the spirito! my invention'.

I claim:

1. The method or simultaneously cracking naphtha and gas oil or oil of higher gravity in the vapor phase by the aid of a heatedheat-car rier gas to produce motor fuels which consists in feeding a mixture of said oil and naphtha to a vaporizer wherein the naphtha isfpresent in 7o suiiicient quantity to lower substantially the partial pressure of said gas oil. superheating the vapor produced, then. efl'ectingcracking of the vapor by mingling it in a 'reaction chamber with the necessary quantity of the heated heat-car- 15 able as motor fuels.

2. The method of simultaneously cracking naphtha and gas oil or oil of higher gravity in the vapor phase by the aid of a heated heat-carrier gas to produce motor fuelswhich consists in feeding a mixture' of said oil and naphtha to a vaporizer wherein the naphtha is present in vsuilcient quantity to lower substantially the partial pressure of said gas oil, superheating the vapor produced, then eiecting cracking of the vapor by mingling it -in a. reaction chamber with the necessary quantity' of the heated heat-carrier gas, then vafter the reaction has taken place passing the mixture from the chamber, dephleg- .mating said mixture by mingling therewith at least Ia. portion of the gas oil fed. to the system under conditions as to vaporize the constituents of the gas oil which it is desired to pass to the vaporizing zone, rectifying the overhead vapor mixture and passing the condensed gas oil fractions to the vaporizer.

3. 'Ihe method according to claim 2 in which no naphtha is fed to the dephlegmating or scrubbing chamber and in which the cracking reaction is continued until substantially al1 of the naphtha is converted so as to render the final product freeV of uncracked or unconverted naphtha.

4. The process according to claim 2 ,in which the temperature of the reaction is carried out at a slightly higher temperature than the temperature at which the gas oil would have been cracked had the naphtha not been present.

5. 'I'he method of simultaneously cracking stantially that of the capacity of the naphtha and gas oil or oil of higher gravity in the vapor phase by the aid of a heated heat-carrier gas which consists in feeding the mixture of said oil and naphtha to a vaporizer, the gas oil being in anamount substantially that of the 5 capacity of the vaporizer when the gas oil alone is Vaporized and the naphtha being in an amount from 5 to 25 by Weight of the gas oil fed to said vaporizer, vaporizing said mixture, superheating the produced vapors of the naphtha and gas oil, then effecting cracking of the mixed vapor by mingling it in a reaction chamber with the necesvsary quantity of heated heat-carrier gas, then after the reaction has taken place passing the mixture from the chamber and separating therefrom the components suitable as motor fuels.

6. lThe method of simultaneously cracking naphtha and gas oil or oil of high gravity in the vapor phase by the aid of a heated heat-carrier gas which consists in feeding the mixture to a I vaporizer, the gas oil being in an amount subvaporizer when the gas oil alone is vaporized and the naphtha being in an amount from 5 to around 25% by Weight of the gas oil fed to said vaporizer, vaporizing said mixture, superheating .the produced vapors oi' the naphtha and gas oil at a temperature from 850 to 965 F., effecting cracking of the mixed vapor by mingling it in a reaction chamber with the necessary quantity of heated heat-carrier gas so as to produce a cracking temperature of from 950 to 1050 F., then after the reaction has'taken place-passing the mixture to the chamber and separating the components suitable as motor fuels.

ALBERT P. SACHS. 

